In the manufacture of seamless and welded tubing, it is a conventional practice to initially form the tubing to a larger diameter and with a greater wall thickness than is generally desired. Among the finishing operations to which this tubing is subjected frequently is reduction in size in a stretch reducing mill. The stretch reducing mill typically consists of a series of consecutive mill stands of progressively decreasing diameter, arranged with individual drives, such that each stand is operated at a higher speed than the previous stand. The arrangement is such that, not only is the diameter of the tubing progressively reduced from stand to stand, but the tubing is also placed under controlled tension between stands, resulting in a controlled elongation of the tubing over and above that which would normally result from the fact of the tube being reduced in diameter. By properly relating the reduction in diameter to the elongation, the finished tubing may be controlled both as to its outside diameter and as to its wall thickness.
Since a standard size of incoming tubular stock is customarily processed into finished tubing of various sizes and wall thicknesses, it is generally necessary to set up the stretch reducing mill so as to accommodate relatively frequent reorganization. Typically, this is accomplished by removably mounting the individual mill stands in a base or foundation structure. When it is desired to change over the mill from one size of finished tubing to another, the existing combination of mill stands is removed and replaced by another combination, which is appropriate to the intended new production. Pursuant to the present invention, improvements are provided in the construction of a stretch reducing mill, which greatly facilitate the changeover of the mill from one mill stand combination to another. Thus, providing improved flexibility in production scheduling, while at the same time providing for down time of the mill to be kept at a practical minimum.
According to one of the more specific aspects of the invention, a multi-stand stretch reducing mill is provided in which a series of adjacent mill stands are secured at the top to a massive, retaining beam, which extends the full length of the mill, over the tops of the individual mill stands. The retaining beam is connected or arranged to be connected to each of the mill stands and thus can serve as a means for simultaneously lifting all of the mill stands out of the foundation and conveying them to the preparation floor. This retaining beam, because of its inherent massive weight, serves, when the mills are in working position, to assist in holding the mill stands in place on the mill foundation. In addition, the retaining beam serves as a medium to which vertically downward clamping force may be applied to the individual mill stands, through a relatively limited number of high power clamping devices. By serving in a dual capacity of a hold-down means and also a lifting and carrying means, the massive retaining beam enables the changeover of the mill to be accomplished quickly and with great efficiency.
In accordance with another aspect of the invention, an improved arrangement is provided for longitudinally clamping into the mill foundation a series of individual mill stands. The improved arrangement comprises a series of hydraulic cylinders, arranged in a configuration to correspond to the alignment of spacing bosses provided on each of the mill stands. In conjunction with the several hydraulic cylinders, there is provided a heavy-duty mechanical locking mechanism, which is activated after the mill stands have been hydraulically clamped. In normal operations, the mechanical locking system functions only in a standby capacity. However, should there be a failure or reduction in the hydraulic clamping pressure during operation of the mill, the standby mechanical locking system will prevent any significant displacement of the mill stands, which might otherwise result in serious damage to the mill.
In accordance with a further specific aspect of the invention, an improved and simplified arrangement is provided for effecting the coupling and decoupling of the individual mill stands to their respective drive motors when changing over the mill. The improved arrangement is in the form of a common clutch beam, which extends along the full length of the mill and is carried by a series of crank levers. The series of levers is actuated simultaneously, by actuation of a longitudinally extending tension bar, so that the clutch beam is caused to move transversely with respect to the mill axis to effect declutching. Since a mill of typical construction utilizes alternate high and low drive inputs, the clutch beam assembly of the invention is arranged to extend along the mill between the levels of the upper and lower drives and is provided with alternately upwardly and downwardly extending clutching yokes for engagement with the alternate high and low mill drives.
The prior art considered to be of interest includes the William R. Scheib U.S. Pat. No. 3,328,973, assigned to Aetna-Standard Engineering Co., a subsidiary of White Consolidated Industries, Inc. General features of the mill arrangement are also shown in the Gillet U.S. Pat. No. 3,355,923, the Chang U.S. Pat. No. 3,221,529, and the Kocks U.S. Pat. No. 2,214,279.
For a better understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of a preferred embodiment, and to the accompanying drawings.